First off, Anakin has the high-midichlorian count of ANYONE, not just Jedi. If you're referring to the 1st highest Sith as Palpatine, I believe that's inaccurate. While we haven't had specific information about Palpatine's midichlorian count, it is reasonable to suppose that Anakin's was still higher. They remarked how he'd had the highest count ever found by the Jedi in TPM, and since he's the Chosen One, that would imply a significance to his power/potential i.e. he really DOES have the highest midichlorian count.

Also, in AotC, Palpatine tells Anakin, "I foresee you will become the greatest of all the Jedi, even more powerful than Master Yoda." In RotS, he tells Yoda, "Lord Vader will become more powerful than either of us."

Now, on to the meat of the question.

The high ground is an answer inconsistent with TPM - Maul had the high ground, yet Obi-wan was able to leap out and slice 'n' dice without being skewered himself.

The better answer is Anakin's anger and inexperience.

Remember, despite his high midichlorian count, he was said that he could/would BECOME more powerful than Yoda or Palpatine. Midichlorians are POTENTIAL, not current level of power.

However, the line between skill/experience and raw power has always been a murky one in the EU. Obviously, despite his inexperience, in AotC Anakin is noted to be extremely capable, probably due to the edge his high count gives him.

In the Episode III game, Anakin performs a move in mid flight to prevent his arm and legs from being severed. Somehow he managed to evade the critical strikes and kill Obi Wan. Is it not plausible that Anakin exposed too much of himself when he leapt?

I fought on the battlefield. I retired to embrace a life of discovery and profit. I carve my own path in life and am better for it.

Maybe he felt that if he stalled the fight long enough, Obi-wan would accept his offer to run away
Maybe he was to arrogant and was not concentrating
Maybe he was to caught up in what he would be or could be if he won

Obi Wan was the greatest master of the Soresu form of lightsaber combat, which focused on defense and energy conservation. He let Anakin bash against his defenses until he became frustrated and tired. Combined with Anakin's arrogance, this frustration led him to make the fateful mistake of leaping to attack Obi Wan.